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PIKK-dependent phosphorylation of Mre11 induces MRN complex inactivation by disassembly from chromatin

Michela Di Virgilio1, Carol Y Ying, Jean Gautier

  • 1Institute for Cancer Genetics, Department of Genetics and Development, and Herbert Irving Comprehensive Cancer Center, Columbia University Medical Center, 1130 St. Nicholas Avenue, New York, NY 10032, USA.

DNA Repair
|August 28, 2009
PubMed

Insights

Mre11 phosphorylation by PIKKs causes the MRN complex to detach from DNA, impacting DNA double-strand break repair. Impaired Mre11 dephosphorylation disrupts ATM signaling, affecting cellular response to DNA damage.

Area of Science:

  • Molecular Biology
  • Cellular Biology
  • Genetics

Background:

  • The cellular response to DNA double-strand breaks (DSBs) is crucial for maintaining genomic stability.
  • The Mre11-Rad50-Nbs1 (MRN) complex plays a key role in sensing and initiating repair of DSBs.
  • The precise role of Mre11 phosphorylation in DSB response pathways remains incompletely understood.

Purpose of the Study:

  • To investigate the functional consequences of Mre11 phosphorylation at SQ/TQ motifs by PI3 Kinase-related Kinases (PIKKs).
  • To elucidate the impact of MRN complex dynamics on DNA damage signaling pathways, particularly ATM activation.
  • To characterize the interplay between Mre11 phosphorylation, MRN complex chromatin association, and DNA damage signaling.

Main Methods:

  • Biochemical assays to analyze Mre11 phosphorylation and its effect on DNA binding affinity.
  • Cellular assays to monitor MRN complex localization and dissociation from chromatin upon DNA damage.
  • Analysis of ATM (Ataxia-Telangiectasia mutated) signaling activation and its regulation by Mre11 dephosphorylation.

Main Results:

  • Phosphorylation of Mre11 at SQ/TQ motifs by PIKKs reduces its affinity for DNA, leading to MRN complex dissociation from chromatin.
  • Mre11 phosphorylation at these sites is not essential for the initial activation of ATM by DSBs.
  • Inhibition of Mre11 dephosphorylation significantly impairs ATM signaling, indicating a role in sustained DNA damage response.

Conclusions:

  • DNA damage-induced Mre11 phosphorylation serves as a regulatory mechanism controlling MRN complex chromatin association.
  • MRN complex inactivation through phosphorylation contributes to the down-regulation of DNA damage signaling during checkpoint recovery.
  • These findings offer insights into the dynamic regulation of DSB repair and checkpoint control.

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